System Design Concepts and Interview FAQs

System Design involves creating the architecture of a system, considering aspects like scalability, reliability, performance, and maintainability. Here are some core concepts and industry-standard architectures:

Core Concepts in System Design

• Scalability: The ability of a system to handle increased load by adding resources.
  • Vertical Scaling: Adding more power (CPU, RAM) to an existing machine.
  • Horizontal Scaling: Adding more machines to handle the load.
• Reliability: Ensuring the system operates correctly even in case of failures.
  • Redundancy: Duplicate critical components or functions to increase system reliability.
  • Failover: Automatic switching to a backup system if the primary system fails.
• Performance: The system’s ability to handle requests within acceptable time limits.
  • Caching: Storing frequently accessed data in a temporary storage for quick retrieval.
  • Load Balancing: Distributing incoming network traffic across multiple servers.
• Maintainability: Ease of making changes and extending the system.
  • Modular Design: Dividing a system into smaller, manageable modules.
  • Documentation: Keeping detailed and up-to-date documentation of the system.
• Security: Protecting the system and data from unauthorized access and breaches.
  • Authentication: Verifying the identity of users or systems.
  • Authorization: Granting permission to resources based on user roles.

Industry-Standard System Design Architectures

• Monolithic Architecture: All components of the system are packaged together.
  • Easy to develop and deploy initially but can become difficult to manage and scale as the system grows.
• Microservices Architecture: Breaks down a system into smaller, independent services that communicate via APIs.
  • Facilitates scalability, maintainability, and allows teams to work independently.
• Event-Driven Architecture: System components communicate through events, enabling asynchronous processing.
  • Useful for applications with complex workflows and real-time updates.
• Service-Oriented Architecture (SOA): Similar to microservices but with more emphasis on service reusability and communication via an enterprise service bus (ESB).
  • Common in large enterprises with complex IT landscapes.
• Serverless Architecture: Applications are deployed on third-party servers and managed by cloud providers.
  • Simplifies operations, reduces costs, and allows developers to focus on code without worrying about infrastructure.
• Layered (N-Tier) Architecture: Organizes the system into layers (presentation, business logic, data access).
  • Promotes separation of concerns and ease of maintenance.
• Peer-to-Peer (P2P) Architecture: Decentralized architecture where each node (peer) can act as both a client and server.
  • Common in file-sharing and blockchain technologies.
• Client-Server Architecture: Divides the system into two parts: client (frontend) and server (backend).
  • The server provides services to client requests, commonly used in web applications.

Popular System Designs

• URL Shortener (e.g., bit.ly)
  • Generate a short, unique alias for a long URL.
  • Handle redirects efficiently.
• Designing a Web Crawler
  • Traverse the web to collect information for indexing.
  • Handle distributed crawling and data storage.
• Social Media Feed (e.g., Twitter, Facebook)
  • Display posts from friends/followed users.
  • Efficiently update and retrieve feed content.
• Messaging System (e.g., WhatsApp, Facebook Messenger)
  • Real-time messaging between users.
  • Manage message delivery, read receipts, and offline storage.
• Distributed File Storage (e.g., Google Drive, Dropbox)
  • Store and retrieve large amounts of data.
  • Handle replication, consistency, and data retrieval.
• Ride Sharing Service (e.g., Uber, Lyft)
  • Match riders with drivers in real-time.
  • Handle location tracking, ride pricing, and user management.
• Video Streaming Service (e.g., YouTube, Netflix)
  • Stream video content to users.
  • Handle video storage, encoding, CDN distribution, and playback.
• E-commerce Platform (e.g., Amazon, eBay)
  • Manage product listings, shopping carts, and orders.
  • Handle search, recommendation, and payment processing.
• Search Engine (e.g., Google)
  • Index and search the web for relevant information.
  • Handle ranking algorithms, crawling, and query processing.
• Notification System (e.g., Email , SMS notifications)
  • Send notifications to users.
  • Handle user preferences, delivery guarantees, and scaling.

FAQs in System Design Interviews

• What is the difference between vertical and horizontal scaling?
  • Vertical scaling involves adding more resources (CPU, RAM) to an existing machine.
  • Horizontal scaling involves adding more machines to handle the load.
• How would you design a system to handle a large number of read/write operations?
  • Use caching to reduce read load.
  • Implement sharding to distribute the write load.
  • Consider using a NoSQL database for high write throughput.
• How do you ensure high availability in a distributed system?
  • Implement redundancy and failover mechanisms.
  • Use load balancers to distribute traffic.
  • Design for fault tolerance by replicating data across multiple nodes.
• What is eventual consistency?
  • Eventual consistency means that, given enough time, all replicas of a distributed system will converge to the same state.
• How would you design a rate limiter?
  • Use techniques like token bucket or leaky bucket.
  • Store rate limiting information in a distributed cache (e.g., Redis).
• What are the trade-offs between consistency and availability in a distributed system?
  • According to the CAP theorem, you can only achieve two out of three: consistency, availability, and partition tolerance.
  • Choosing consistency means you may sacrifice availability during network partitions.
  • Choosing availability means you may have eventual consistency.
• How would you design a scalable search engine?
  • Use inverted indexes for fast search lookups.
  • Implement distributed crawling and indexing.
  • Use ranking algorithms to provide relevant search results.
• What is a CDN and how does it work?
  • A Content Delivery Network (CDN) caches content at various edge locations to reduce latency and load on the origin server.
  • It helps in faster content delivery by serving content from a location closer to the user.
• How do you handle database replication?
  • Use master-slave replication or master-master replication.
  • Ensure data consistency with techniques like two-phase commit or conflict resolution strategies.
• What are the considerations for designing a caching system?
  • Decide what data to cache based on access patterns.
  • Choose an appropriate eviction policy (e.g., LRU, LFU).
  • Handle cache invalidation strategies to maintain data consistency.

These examples and questions should give you a good foundation for understanding system design and preparing for interviews.

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